Radioreceiver



1935- H. J. LOFTIS RADIORECEIVER Fil'ed May 51, 1930 INVENTOR ZwflerJLy/z s BY ATTORNEY Patented Dec. 31, 1935 PATENT OFFICE RADIORECEIVER Homer J. Loftis, Dayton, Ohio, assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application May 31, 1930, Serial No. 457,738

Claims.

This invention relates to a manual volume control of a radioreceiver and more particularly to a volume control that adjusts the bias supplied to an electrode simultaneously with the adjustment 5 of a resistance that by-passes a predetermined amount of the incoming signal.

It is an old and well known expedient to change the volume of a radioreceiver by adjusting the bias or potential supplied to one of the electrodes in a vacuum tube. It is also old to by-pass a portion of the incoming signal to ground thereby reducing the volume. Each of these expedients have been separately adjusted. This has its disadvantages especially where a switch is used to close or open a by-pass circuit in the antenna, in that the switch upon being actuated especially by an inexperienced operator may cause overloading of the radioreceiver. It can be readily seen that if the radioreceiver is set for a suitable volume output with the by-p-ass circuit closed so that only a small portion of the signal is actually fed into the radioreceiver that upon the opening of the circuit the volume will be increased tremendously so as to overload the radioreceiver and so as to cause discomfort to the audience.

An object of this invention is to control the volume output by adjusting the bias supplied to an electrode and by adjusting the amount of signal current by-passed in the antenna circuit from a single control knob so that they may be operated simultaneously and in synchronism.

Another object of the invention is to provide a by-pass for the radioreceiver which may be adjusted so as to b-y-pass only a very small per cent of the incoming signal to practically all of the incoming signal. This has been accomplished by providing a variable resistance in the by-pass circuit which may be adjusted from a maximum resistance to practically no resistance.

Another object of this invention is to provide a loading inductance in the antenna circuit so that the performance of the radioreceiver will be substantially the same regardless of the constants of the receiving portion of the antenna which varies due to local conditions in every particular hook- Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of one form of the present invention is clearly shown.

In the drawing:

The single figure discloses an antenna circuit and two stages of radio frequency amplification of a radioreceiver.

The reference character N] indicates the receiving portion of an antenna connected to the terminal I 2. A condenser l4 having one terminal connected to terminal l2 has the other terminal connected to a resistance I6 and to coils l8 and 20 connected in parallel with the resistance Hi. The loading coil l8 has been inserted in the antenna circuit so as to provide an antenna with a very high inductance thereby reducing the effect of the variable constants due to the irregularity of the external antenna.

The coil 20 forms a primary winding of a radio frequency transformer 22 having the secondary 24 cooperating with the variable condenser 26 to form a resonant circuit for the input to the grid 28 of the first thermionic vacuum tube 30.

A portion of the incoming signal may be bypassed through a portion of the resistance l6 so as to reduce the signal passing through the condenser l4 and the coils I8 and -20 thereby reducing the volume of the radioreceiver. As clearly indicated the amount of this signal may be changed by varying the tap 32 on the resistance I6. The tap 32 is mounted on a movable 'mechanism indicated schematically by the insulating bar 33. This resistance is so constructed and arranged that a considerable movement of the tap 32 near the upper end 34 causes substantially no change in the resistance whereas a slight movement of the tap 32 along the resistance l6 near the end 36 changes the resistance very much, for reasons which will appear more fully later on.

The volume output of the radioreceiver may also be varied, as is well known, by changing the bias supplied to the control electrode 28 or by changing the bias sup-plied to the screen grid or space charge electrodes 38. In the preferred modification the space charge electrode 38 of the first or of the first two or more stages may be adjusted by varying the resistance 40, having one end connected to a suitable source of potential and the other end grounded through the resistance M. The resistance 40 may be adjusted by changing the tap 42 insulatingly mounted on the bar 33 so as to either increase or decrease the resistance in series with the electrode or electrodes and the source of potential. The resistance 40 has been so constructed and arranged that a very small movement in the upper end 44 as viewed in the single figure makes a very large difference in resistance While a change of equal magnitude near the lower end 46 causes very littl change in resistance.

As indicated schematically, the taps 32 and 42 may be lowered or raised along the resistances It and 49 respectively, in unison from a single control knob, not shown, actuating the bar 33.

Operation From the foregoing description, it can be clearly seen that as the taps 32 and 42 are moved downwardly from the tops of the resistances I6 and 40, as seen in the single figure, and as indicated by the reference characters 32 and 42, the bias supplied to the electrodes 38 will be decreased thereby reducing the volume output without by-passing any great amount of the current in the antenna circuit. When the taps 32 and 42 approach the lower portions 36 and 46 of the resistances i6 and 45 respectively, the rate of change for each increment of movement of the control knob will make practically no difference in the bias supplied to the electrodes 38, but a very great amount of difference in the amount of current by-passed from the primary 20. This structure as clearly seen will first reduce the volume by changing the bias supplied to the electrode 38 as far as is consistent with the proper functioning of the tubes and then it will change the amount of current by-passed from the primary 2!} so as to further reduce the volume output or vice versa, each of said adjustments being controlled by a single control knob.

While the form of embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. An antenna circuit for a radioreceiver comprising a signal receiving antenna, a loading coil connected to the antenna through a condenser, a coupling unit for connecting the antenna circuit to a radioreceiver, and a by-pass circuit including a potentiometer connecting one terminal of said condenser to ground and a lead connected to the opposite terminal of the condenser and to the adjustable terminal on the potentiometer arranged to short circuit said condenser when substantially no signal current is by-passed.

2. An antenna circuit for a radioreceiver comprising a signal receiving antenna, a coupling unit for coupling the antenna circuit to said radioreceiver, said coupling unit being connected through an impedance to the antenna, and a by-pass circuit including a grounded potentiometer having one terminal connected directly to the antenna circuit and the adjustable terminal connected so as to shunt said impedance through a portion of the potentiometer so as to by-pass part of the signal currents, said impedance providing the antenna with suflicient inductance so as to compensate for variations in electrical constants of the antenna circuit.

3. In combination with an electrical signal amplifier having an input circuit, an output circuit and at least one space discharge amplifier device interposed between said circuits for the transmission of signals from said input circuit to said output circuit, a signal receiving antenna, a loading coil connected to the antenna through a condenser, a coupling unit for connecting the antenna circuit to the signal amplifier, said loading coil being arranged so as to provide the antenna with sufficiently high inductance so as to compensate for variations in electrical constants of the antenna circuit, adjustable means for varying the transmission efiiciency of said amplifier device between predetermined limits and adjustable means for varying the signal strength applied to said input circuit, said two means being variable simultaneously by a single operating means, the rate of change of said adjustable means for equal increments of movement of the single operating means effecting different degrees of controlling action in such a manner that for successive equal increments of movement of the single operating means the controlling action or one of said variable means decreases While the controlling action of the other of said variable means increases.

4. In combination with an electrical signal amplifier having an input circuit, an output circuit and at least one space discharge amplifier device interposed between said circuits for the transmission of signals from the input circuit to the output circuit, a signal receiving antenna, a loading coil connected to the antenna through a condenser, said loading coil having an inductance value to provide the antenna with sufiicient inductance so as to compensate for variations in electrical constants of the antenna circuit, a coupling unit for connecting the antenna circuit to the amplifier, means provided with an element movable between said limits to vary the trans mission efficiency of the amplifier device, a second means provided with an element movable between certain limits to vary the signal strength applied to th input circuit, said two movable elements being variable simultaneously by a single operating means, the rate of change of both of said means for successive equal increments of movement of the single operating means therefor in one direction effecting increasing degrees of controlling action by one of said variable means and decreasing degrees of controlling action by the other of said variable means.

5. The system described in the next preceding claim wherein the first and second named means comprise resistance windings having a variable pitch.

HOMER J. LOFTIS. 

